The invention relates generally to the production of annular articles. Of special interest is the production of wire races for anti-friction bearings.
Anti-friction bearings provided with wire races which have been bent into a ring-shaped or annular configuration are known. Such anti-friction bearings include one or more ring-shaped tracks for guiding the rolling elements of the bearing, the tracks being provided in the wire races. The tracks are formed with a predetermined bearing contact angle which is the same at each location circumferentially of the race.
Wire races for anti-friction bearings are known wherein the track is formed by a grinding operation. Here, it is also known to subject the race to a finish rolling operation so as to impart to the surface of the track a curvature which corresponds to the radius of the rolling elements, for instance, spherical balls, of the anti-friction bearing.
Wires for use in ball bearings are normally of circular cross-section and the track is formed in the round wire at a predetermined angle by a machining operation after the wire has been bent to an annular configuration. Subsequently, the track is subjected to a grinding operation while maintaining this angle. This method has certain disadvantages. Thus, where grinding of the track is performed on thick wires, large quantities of material must be ground off. Moreover, this manner of treatment is costly and, in addition, causes a distortion of the race as stresses are released during the grinding operation so that the wire must be continuously readjusted. Furthermore, since the wire is hard, the grinding discs required for the grinding operation are subjected to great wear.
In the German Pat. No. 1,525,079, it has been proposed to form the requisite cross-sectional configuration of the wire race by subjecting the wire to a conventional cold-drawing operation. After being drawn in this manner, the wire is bent to annular configuration and, finally, the overlapping ends of the wire are cut off to thereby obtain a wire race. In view of the high tooling costs involved, the use of such drawn wire races is economically feasible only when large quantities of wire races are to be manufactured.
The use of these known production methods becomes even more costly and more difficult where the preparation of races from wire having a wire diameter of 20 to 24 millimeters and greater is concerned and where the wire races are to be used for anti-friction bearings having a diameter of at least 2 meters. Here, bar stock may be used as the starting material. However, the length of such bar stock is usually restricted to a maximum of 6 meters. Consequently the use of wire races made from such starting material is restricted to anti-friction bearings having a diameter of at most about 1.9 meters since, for anti-friction bearings of larger diameter, it then becomes necessary to place individual wire race pieces or segments next to one another in order to form a ring which is substantially circumferentially complete. In such an event, the disadvantages associated with the use of individual segments must be coped with.
The problems just outlined may be overcome by starting from a wire coil rather than from bars of restricted length. However, if wires which have been drawn so as to impart to them the desired profile are wound into the form of a coil subsequent to the drawing operation, there exists the danger, particularly for wires of larger cross-section, that the profiles which are to serve as tracks for the rolling elements of the bearing will be damaged when the wire is unwound and is straightened in the conventional straightening apparatus. Since the wire is drawn to its final dimensions, further processing of the wire is not possible. Thus, if damage occurs, the wires cannot be used. This danger may be lessened by using round or semi-circular wires as starting material and providing these with tolerances at the track surface before winding them into a coil. This procedure, however, requires additional processing of the wire after it has been unwound.